Fig. 1. Live analyses of cell-cycle durations of histone-GFP embryos between cycles 6 and 13. (A-H) Different cycle phases of an embryo at cycle 8. (A) The earliest interphase (000 seconds); (B) last interphase image recorded (230 seconds). Ten seconds later (C), nuclei are in prophase, which is characterized by punctuated GFP signal and loss of the round nuclear morphology. At 440 seconds (D), an obvious metaphase configuration is established and 10 seconds later sister chromatids begin to separate (E), indicating the beginning of anaphase. Between 550 and 600 seconds, nuclei progress from anaphase (F, clear teardrop shape) to telophase (G, more rounded). Ten seconds later (H, 610 seconds), the beginning of interphase of cycle 9 is observed. With this information, we calculated durations of total cell cycles, interphases, prophase-metaphases and anaphase-telophases between cycles 6 and 13. (I) Overall cell-cycle and interphase duration between cycles 6 and 13, based on time-lapse recordings of 39 embryos. For each cycle, number of embryos (N) differs because the quality of recordings improves after cycle 5; before cycle 5, abundant maternal loading of histone-GFP obscures the chromosomal histone-GFP. All data points are aligned at cycle 9, when nuclei migrate to the cortex and pole buds are formed (Foe and Alberts, 1983). Because the preblastoderm cycles are not exactly synchronous (Fig. 2), cell-cycle-phase duration within each cycle was defined as the average of 1-2 nuclei in the middle with 1-2 nuclei in the posterior region of each embryo. (J) Interphase durations of grp¹ embryos do not differ from wild-type embryos before cycle 11. The number of grp¹ embryos (N') is shown in J; data for wild-type embryos are taken from I. Scale bar: 30 µm.